The present application relates generally to micro assemblies. It finds particular application in conjunction with micro-assembly techniques used for fabricating micro assemblies, and will be described with particular reference thereto. However, it is to be appreciated that the present application is also amenable to other like applications.
Micro assembly pertains to assembling micro objects into micro assemblies. Micro objects are typically a few microns to 100s of microns in size (e.g., 1-500 microns in length, width or area) and include, for example, microchips. One technique for micro assembly employs electrostatic or magnetic fields to manipulate micro objects. In this technique, patterns are first electrostatically or magnetically encoded on the micro objects. Thereafter, the patterns are used for manipulation of the micro objects in electric or magnetic fields. The patterns can also be used for identifying and/or matching micro objects, similar to biological molecular recognition.
One challenge with the above-referenced technique pertains to accurately moving micro objects in the presence of stiction. Stiction is the difference between the coefficient of static friction and dynamic friction resulting from the intermolecular forces between the two contacting surfaces. When attempting to move a micro object in the presence of stiction, the forces required to initiate motion are often significantly greater than the forces required to maintain motion. As a result, attempts at fine control over the position of a micro object subject to stiction often result in ringing, overshoot and instabilities in the control.
Another challenge with the above-referenced technique pertains to patterning micro objects. Many different techniques exist for patterning, including techniques based on chemical means, such as dielectric additives enabling positive or negative charge build up on micro objects, and techniques based on physical means, such as corona charging. The known techniques commonly used today can be broken into two distinct groups. The first group uses Gyricon bichromal spheres, which develop a dipole when suspended in an electrolyte due to different zeta potentials of the surfaces of the two hemispheres. The second group uses electrophoretic ink consisting of two types of oppositely charging particles. Known examples of these two groups are believed to use proton exchange based on different acidity levels of the chemical agents. Further, some of these examples are believed to be based on tribocharging. However, tribocharging and proton exchange with electrolytes are somewhat uncontrolled and immersion in electrolytes leads to complications from ion screening.
A micro assembler employing the above-referenced technique is described in U.S. Patent App. Pub. No. 2009/0218260. The micro assembler positions and orients patterned micro objects on an intermediary substrate using a planar electrode array. Thereafter, the micro objects are transferred to a final substrate for planarization and wiring. This micro assembler requires the electrode array to be permanently affixed to the substrate upon which the micro objects are manipulated, thereby necessitating both the intermediary substrate and the final substrate.
The present application provides new and improved methods and systems which improve on the above-referenced technique and address the above-referenced challenges.